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The cysteine sulfhydryl group is nucleophilic and easily oxidized. The reactivity is enhanced when the thiol is ionized, and cysteine residues in proteins have pK a values close to neutrality, so are often in their reactive thiolate form in the cell. [23] Because of its high reactivity, the sulfhydryl group of cysteine has numerous biological ...
The −SH functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols (that is, sulfur takes the place of oxygen in the hydroxyl ( −OH ) group of an alcohol), and the word is a blend of " thio- " with "alcohol".
This reaction is rapid and stoichiometric, with the addition of one mole of thiol releasing one mole of TNB. The TNB 2− is quantified in a spectrophotometer by measuring the absorbance of visible light at 412 nm, using an extinction coefficient of 14,150 M −1 cm −1 for dilute buffer solutions, [4] [5] and a coefficient of 13,700 M −1 cm −1 for high salt concentrations, such as 6 M ...
Cysteine has a very reactive sulfhydryl group on its side chain. A disulfide bridge is created when a sulfur atom from one Cysteine forms a single covalent bond with another sulfur atom from a second cysteine in a different part of the protein. These bridges help to stabilize proteins, especially those secreted from cells.
The sulfhydryl group is a key player can is found in cysteine bridges on proteins and reagents like Traut’s reagents, SATA, and Sulfo-LC-SPDP. [6] The reduction or hydrolysis of these groups generates thiol groups that create antibody conjugation to lipids. [ 6 ]
A unique intramolecular cysteine disulfide bonds in the ATP-binding domain of SrrAB TCs found in Staphylococcus aureus is a good example of disulfides in regulatory proteins, which the redox state of SrrB molecule is controlled by cysteine disulfide bonds, leading to the modification of SrrA activity including gene regulation.
The second step transfers ubiquitin to an active site cysteine residue, with release of AMP. This step results in a thioester linkage between the C-terminal carboxyl group of ubiquitin and the E1 cysteine sulfhydryl group. [16] [54] The human genome contains two genes that produce enzymes capable of activating ubiquitin: UBA1 and UBA6. [55]
NEM has been widely used to probe the functional role of thiol groups in enzymology. NEM is an irreversible inhibitor of all cysteine peptidases, with alkylation occurring at the active site thiol group (see schematic). [3] [4] Mechanism of irreversible inhibition of a cysteine peptidase with NEM.